Convert well GPM into hours (and days) to apply a target depth of water over a field acreage.
Use this when your pump/well flow is known in gallons per minute and you need a set time to put on 0.5–1.5 inches for pasture, hay, or garden blocks.
One acre-inch is about 27,154 gallons. Runtime = (acres × inches × 27,154) ÷ (GPM × 60).
Gross water needed rises when efficiency is below 100% (drift, overlap, evaporation).
gallons = acres × inches × 27,154 ÷ (efficiency% ÷ 100)
hours = gallons ÷ (GPM × 60)
days @ 24h = hours ÷ 24
Pair with drip-tape set time when you irrigate by zone tape rather than broadcast GPM.
2 acres × 1.0 in × 27,154 = 54,308 gal net. At 75% efficiency → 72,411 gal. At 15 GPM: 72,411 ÷ (15×60) ≈ 80.5 hours (~3.4 days continuous).
Assumptions: constant GPM; efficiency captures distribution losses you choose.
Limits: does not check well recovery, drawdown, or nozzle charts. Continuous multi-day runs may overheat pumps.
Responsibility: respect water rights and pump duty ratings; verify GPM with a meter or timed tank fill.
About 27,154 gallons — the water to cover one acre one inch deep.
Acres = sq_ft ÷ 43,560. A 4,356 sq ft plot is 0.1 acre.
Use a higher efficiency for well-managed drip (often 85–95%) than impact sprinklers.